In recent years, the use of an optical waveguide has been spreading as a means for guiding an optical signal from one point to another. The optical waveguide comprises a linear core portion and a clad portion surrounding the core portion. The core portion is formed of a material which is substantially transparent to light, and the clad portion is formed of a material having a lower refractive index than the core portion.
In the waveguide, the light introduced into the waveguide from one end of the core portion is transmitted to another end of the core portion while being reflected at the interface between the core portion and the clad portion. When the waveguide is used, a light emitting element such as a semiconductor laser is provided near the light incident side of the waveguide, and a light receiving element such as a photo diode is provided near the light emission side of the waveguide. The light emitted from the light emitting element enters and travels in the waveguide, and is received by the receiving element. Through such a waveguide, a communication is performed based on the intensity or blink pattern of the light.
Substituting the electric wiring of a signal processing board with the waveguide, for example, solves a problem peculiar to an electrical signal such as generation of a high-frequency noise or degradation of the electrical signal; therefore, such substitution with the waveguide is expected to further enhance the throughput of the signal processing board.
For substituting the electric wiring with the waveguide, a mutual exchange between electrical signal and optical signal is necessary. For this purpose, a waveguide module provided with the waveguide optically connecting the light emitting element and the light receiving element is being developed.
For example, Patent Document 1 describes an optical interface having a printed board, a light emitting element on the printed board, and an optical waveguide formed on the lower surface of the printed board. Further, the optical waveguide and the light emitting element are optically connected through the through hole formed on the printed board for transmitting the optical signal.
In the optical interface as described above, it is necessary to divert the path of light by a mirror formed in the waveguide for making the signal light emitted from the emission portion of the light emitting element enter the core portion of the waveguide.
The mirror as described above may be, for example, one configured to have an inclined plane traversing only the waveguide in the core portion thereof, or may be one configured to have an inclined plane as described in Patent Document 2, which is continuously formed from the core portion to the clad layer laminated thereon. Patent Document 2 discloses a technique in which an under clad layer, a core and an over clad layer are laminated together, followed by providing at one end of the resulting laminate an inclined plane which is inclined relative to the axial direction of the core, i.e. the longitudinal direction, with an inclination angle of 45°, where the inclined plane is utilized as a light reflecting surface of a waveguide.